Update dependency tornado to v6.4.2

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
tornado (source)	==6.4.1 -> ==6.4.2

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Release Notes

tornadoweb/tornado (tornado)

### [`v6.4.2`](https://redirect.github.com/tornadoweb/tornado/compare/v6.4.1...v6.4.2) [Compare Source](https://redirect.github.com/tornadoweb/tornado/compare/v6.4.1...v6.4.2)

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Configuration

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